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15-441 Computer Networking

15-441 Computer Networking. Data and Control Planes. Goals of This Lecture. Show h ow everything fit together Review data plane components v arious switching architectures Head of line blocking Scheduling Header lookup Discuss Control plane Control processor Routing protocol

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15-441 Computer Networking

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  1. 15-441 Computer Networking Data and Control Planes

  2. Goals of This Lecture • Show how everything fit together • Review data plane components • various switching architectures • Head of line blocking • Scheduling • Header lookup • Discuss Control plane • Control processor • Routing protocol • Signaling protocol • Interconnection of Multiple control protocols

  3. Switches circuit switch Ethernet switch ATM switch IP router Switch fabric high capacity interconnect Line card address lookup in the data path (forwarding) Control Processor load the forwarding table (routing or signaling) Control Processor Switch Fabric Line Cards Line Cards Review: Structure of A Generic Communication Switch

  4. Data and Control Planes • Data plane: how each packet is processed? • Forwarding: header lookup and forward the packet to right output port • Switching: move packets from input port to output port • Scheduling: manage buffer and bandwidth resource • Control plane: how forwarding tables are computed • Router: routing protocols • ATM and phone switches: signaling & routing protocols • Ethernet switch: learning and spanning tree

  5. Input and output interfaces are connected through an interconnect A interconnect can be implemented by Shared memory Shared bus Crossbar or other switching fabric Review: Data PlaneSwitch input interface output interface Inter- connect

  6. Cannot be transferred because is blocked by red cell Cannot be transferred because output buffer overflow Review: Head-of-line Blocking • The packet/cell at the head of an input queue cannot be transferred, thus blocking the following packets/ cells Input 1 Output 1 Input 2 Output 2 Input 3 Output 3

  7. Review: Solution to Avoid Head-of-line Blocking • For each input card, maintain at each input N virtual queues, i.e., one per output Input 1 Output 1 Output 2 Input 2 Output 3 Input 3

  8. Input Interface • Packet forwarding: decide to which output interface to forward each packet based on the information in packet header • Examine packet header • Lookup in forwarding table • Update packet header input interface output interface Inter- connect

  9. Circuit Switching Switch Input Ports Output Ports Connects (electrons or bits) ports to ports

  10. E VC3 VC3 VC7 C VC4 B A VC2 VC5 VC2 VC3 VC5 D VC3 F Virtual Circuit Switching: Label Swapping Table at Node A

  11. 12.82.100.101 128.16.120.111 IP Routing • Packet with destination address 12.82.100.101 is sent to interface 2, as 12.82.100.xxx is the longest prefix matching packet’s destination address 128.16.120.xxx 1 12.82.xxx.xxx 3 12.82.100.xxx 2 … … 1 2

  12. Patricia Tries • Use binary tree paths to encode prefixes • Advantage: simple to implement • Disadvantage: one lookup may take O(m), where m is number of bits (32 in the case of IPv4) 1 0 001xx 2 0100x 3 10xxx 1 01100 5 1 0 0 1 0 1 1 2 0 0 3 0 5

  13. Flat address Ethernet: 48 bit MAC address ATM: 28 bit VPI/VCI DS-0: timeslot location Limited scalability High speed lookup Hierarchical address IP <network>.<subnet>.<host> Telephone: country.area.home Scalable Easy lookup if boundary is fixed telephony Difficult lookup if boundary is flexible longest prefix match for IP Review: Addressing and Look-up

  14. Output Interface • Buffer management: decide when and which packet to drop • Scheduler: decide when and which packet to transmit • FIFO, Round Robin, Strict Priority Buffer Scheduler 1 2

  15. Example: FIFO router • Most of today’s routers • Drop-tail buffer management: when buffer is full drop the incoming packet • First-In-First-Out (FIFO) Scheduling: schedule packets in the same order they arrive

  16. Data and Control Planes • Data plane: how each packet is processed? • Forwarding: header lookup and forward the packet to right output port • Switching: move packets from input port to output port • Scheduling: manage buffer and bandwidth resource • Control plane: how forwarding tables are computed • Router: routing protocols • ATM and phone switches: signaling & routing protocols • Ethernet switch: learning and spanning tree

  17. Signaling Protocol for Circuit-Switched and Virtual-Circuit-Switched Networks: • Signaling protocol establishes/tears down circuit • Signaling message are routed • Signaling protocol fills the forwarding table • What tables are maintained by a Circuit Switch processor? • Are there routing protocols? • Parameters used for establishing Virtual Circuits • Source and destination Addresses • Traffic Characteristics • QoS Parameters • Others? • Parameters can be stored in forwarding table to help forwarding decision

  18. Three Classes of Routing Protocols • Distance vector (RIP) • Distributed path computation • Keep only local link data • Bellman-Ford algotrithm • Link state (OSPF, IS-IS) • Local path computation • Distribute all link data -- each node has whole topology • Dijkstra’s algorithm • Path vector (BGP) • Distributed path computation • Distribute routes (prefix + path) to every node --- each node stores all routes subject to policy

  19. Components of IP Control Plane (I) P P BGP OSPF RIB RIP RIB Local RIB OSPF RIB BGP RIB RIP RIB 110 120 RIP Route Selection OSPF Forwarding Information Base A B • Machine : routing control processor • Data structure: RIB (Routing Information Base) • Protocol Instance Module: software module that exchanges messages with protocol instance modules running on other routers

  20. Components of IP Control Plane (II) P P BGP OSPF RIB RIP RIB Local RIB OSPF RIB BGP RIB RIP RIB 110 120 RIP Route Selection OSPF Forwarding Information Base A B • Protocol: define the interaction (message formats, message semantics, timing) among distributed set of protocol instance modules. The goal is to generate a consistent set of local RIBs at each protocol module

  21. Components of IP Control Plane (III) P P BGP OSPF RIB RIP RIB Local RIB OSPF RIB BGP RIB RIP RIB 110 120 RIP Route Selection OSPF Forwarding Information Base A B • Local RIB: routing table entries set by configuration files • Route redistribution: inject routes from one protocol instance module to another protocol instance module (e.g OSPF to BGP) • Route selection: for each prefix, select one among multiple routes (each computed by one protocol instance)

  22. Excerpts from a Router Configuration File • interface Ethernet0 • ip address 6.2.5.14 255.255.255.128 • interface Serial1/0.5 point-to-point • ip address 6.2.2.85 255.255.255.252 • ip access-group 143 in • frame-relay interface-dlci 28 • router ospf 64 • redistribute connected subnets • redistribute bgp 64780 metric 1 subnets • network 66.251.75.128 0.0.0.127 area 0 • router bgp 64780 • redistribute ospf 64 match route-map 8aTzlvBrbaW • neighbor 66.253.160.68 remote-as 12762 • neighbor 66.253.160.68 distribute-list 4 in access-list 143 deny 1.1.0.0/16 access-list 143 permit any route-map 8aTzlvBrbaW deny 10 match ip address 4 route-map 8aTzlvBrbaW permit 20 match ip address 7 ip route 10.2.2.1/16 10.2.1.7

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